A Gas Turbine initially at rest must be provided with means to enable the internal `rotor` to begin its rotation. The rotor initially at rest is supported by `journal bearings` located at each end of the rotor. The journal bearing surfaces are void of lubrication film when the rotor is at rest. Thus, the rotor will require sufficient break-away torque to begin its motion. This torque is provided by the turbines `turning gear` which is comprised of an electric motor linked to the rotor through the use of a speed reduction gearbox. This turning gear in itself will not provide sufficient break-away torque to place the rotor in motion if the rotor was initially stationary and sitting on the journal bearing surface. To lower the required break-away torque and enable the turning gear to place the rotor in motion, the rotor is hydraulically lifted off of the journal bearing surface by turbine lubricating oil (normally 25 psi) which has been `boosted` to a much higher pressure (over 3000 psi) and then jetted into the bottom of the journal bearing.
This boosted high pressure (over 3000 psi) turbine lubrication oil which is jetted into the bottom of the turbine journal bearing is called `lift oil`. There is a system of valves, pumps, filters, manifolds, and tubing which boosts this lubrication oil to high pressure (over 3000 psi) and then delivers it to the bottom of the turbine journal bearing. This system lifts the rotor off of the journal bearing prior to energizing the turning gear thereby reducing the break-away torque below that provided by the turning gear thus enabling rotation. Since this system lifts the rotor through the use of high pressure hydraulic force provided by the lubrication oil, it is often called a `lift oil system`.
In order to position various hydraulic actuators required for the gas turbine operation, the gas turbine lubrication oil is boosted to a pressure of 1600 psi. The system of valves, pumps, filters, manifolds, and tubing which boosts this lubrication oil to 1600 psi and then delivers it to various hydraulic actuators is often called the `hydraulic system`.
Conventionally, both of these systems include complicated manifolds, oil filtration units, and variable volume pumps. Moreover, the standard lift oil system offers no redundancy. Thus, if the pump fails to operate, the gas turbine cannot start up. It has, therefore, been proposed to provide a backup lift oil pump. If a second lift oil pump is provided, however, it must be added to the conventional lift oil system as an option. This leads to significant product variability and the second pump is difficult to install due to limited deckspace availability.